// @ts-nocheck
import { CurveFactory } from 'd3-shape'

function sign(x) {
  return x < 0 ? -1 : 1
}

// Calculate the slopes of the tangents (Hermite-type interpolation) based on
// the following paper: Steffen, M. 1990. A Simple Method for Monotonic
// Interpolation in One Dimension. Astronomy and Astrophysics, Vol. 239, NO.
// NOV(II), P. 443, 1990.
function slope3(that, x2, y2) {
  var h0 = that._x1 - that._x0,
    h1 = x2 - that._x1,
    s0 = (that._y1 - that._y0) / (h0 || (h1 < 0 && -0)),
    s1 = (y2 - that._y1) / (h1 || (h0 < 0 && -0)),
    p = (s0 * h1 + s1 * h0) / (h0 + h1)
  return (
    (sign(s0) + sign(s1)) *
      Math.min(Math.abs(s0), Math.abs(s1), 0.5 * Math.abs(p)) || 0
  )
}

// Calculate a one-sided slope.
function slope2(that, t) {
  var h = that._x1 - that._x0
  return h ? ((3 * (that._y1 - that._y0)) / h - t) / 2 : t
}

// According to https://en.wikipedia.org/wiki/Cubic_Hermite_spline#Representations
// "you can express cubic Hermite interpolation in terms of cubic Bézier curves
// with respect to the four values p0, p0 + m0 / 3, p1 - m1 / 3, p1".
function point(that, t0, t1) {
  var x0 = that._x0,
    y0 = that._y0,
    x1 = that._x1,
    y1 = that._y1,
    dx = (x1 - x0) / 3
  that._context.bezierCurveTo(
    x0 + dx,
    y0 + dx * t0,
    x1 - dx,
    y1 - dx * t1,
    x1,
    y1
  )
}

function MonotoneX(context) {
  this._context = context
}

MonotoneX.prototype = {
  areaStart: function () {
    this._line = 0
  },
  areaEnd: function () {
    this._line = NaN
  },
  lineStart: function () {
    this._x0 = this._x1 = this._y0 = this._y1 = this._t0 = NaN
    this._point = 0
  },
  lineEnd: function () {
    switch (this._point) {
      case 2:
        this._context.lineTo(this._x1, this._y1)
        break
      case 3:
        point(this, this._t0, slope2(this, this._t0))
        break
    }
    if (this._line || (this._line !== 0 && this._point === 1))
      this._context.closePath()
    this._line = 1 - this._line
  },
  point: function (x, y) {
    var t1 = NaN

    ;(x = +x), (y = +y)
    if (x === this._x1 && y === this._y1) return // Ignore coincident points.
    switch (this._point) {
      case 0:
        this._point = 1
        this._line ? this._context.lineTo(x, y) : this._context.moveTo(x, y)
        break
      case 1:
        this._point = 2
        break
      case 2:
        this._point = 3
        point(this, slope2(this, (t1 = slope3(this, x, y))), t1)
        break
      default:
        point(this, this._t0, (t1 = slope3(this, x, y)))
        break
    }

    ;(this._x0 = this._x1), (this._x1 = x)
    ;(this._y0 = this._y1), (this._y1 = y)
    this._t0 = t1
  },
}

function MonotoneY(context) {
  this._context = new ReflectContext(context)
}

;(MonotoneY.prototype = Object.create(MonotoneX.prototype)).point = function (
  x,
  y
) {
  MonotoneX.prototype.point.call(this, y, x)
}

function ReflectContext(context) {
  this._context = context
}

ReflectContext.prototype = {
  moveTo: function (x, y) {
    this._context.moveTo(y, x)
  },
  closePath: function () {
    this._context.closePath()
  },
  lineTo: function (x, y) {
    this._context.lineTo(y, x)
  },
  bezierCurveTo: function (x1, y1, x2, y2, x, y) {
    this._context.bezierCurveTo(y1, x1, y2, x2, y, x)
  },
}

export const monotoneX: CurveFactory = context => new MonotoneX(context)

export const monotoneY: CurveFactory = context => new MonotoneY(context)
